`bdk::Wallet` should have context-specific error types

              I agree that the errors aren't great.

However, I disagree about having a single error enum with a large number of variants. I think we should fix errors in one go with a separate PR, otherwise it's duplicate work.

_Originally posted by @evanlinjin in https://github.com/bitcoindevkit/bdk/pull/976#discussion_r1204823980_
            